1. Technical Field
The present invention relates in general to an improved telecommunications system, and in particular to a method and system for incorporating transport and control facilities for voice, multimedia, and data traffic into a distributed packet-switched core network. More particularly, the present invention relates to a managed, packet-switched core network including multiple nodes which together provide packet-switched management of call setup, mobility, and data transfer for a mobile terminal, thereby providing a packet-switched alternative to a network of circuit-switched Mobile Switching Center/Visitor Location Registers (MSC/VLRs).
2. Description of the Related Art
Utilization of wireless, mobile telephony systems has expanded dramatically in recent years. Such systems typically include cellular or Personal Communication System (PCS) networks. Within such networks, geographic areas are divided into xe2x80x9ccellsxe2x80x9d served by low-power radio transmission facilities. A centralized computer and switching center, known as a Mobile Switching Center/Visitor Location Register (MSC/VLR), controls call setup between a mobile terminal (MT) and either another MT or a terminal linked directly to the Public Switched Telephone Network (PSTN), in addition to providing connectivity to other telecommunications networks.
FIG. 1 is a block diagram illustrative of an example MSC/VLR configuration within a conventional circuit-switched cellular telecommunications system 100. As shown in FIG. 1, telecommunications system 100 includes the network interconnection of a cellular subsystem 101 to a Public Switched Telephone Network (PSTN) 130 and a Public Data Network (PDN) 120. Cellular subsystem 101 is a Code Division Multiple Access (CDMA) wireless communications system in the depicted example. Also within cellular subsystem 101 are mobile terminals (MTs) 126 and 127 which may be handheld cellular phones or other mobile terminal user devices.
Cellular subsystem 101 further includes a Home Location Register (HLR) 104, and a pair or Mobile Switching Centers (MSCs) 102 and 103. Associated to MSCs 102 and 103, are a pair of Visitor Location Registers (VLRs), VLR 132 and VLR 133, respectively. HLR 104 is essentially a customer database within cellular subsystem 101 in which subscriber profile information for MTs, such as MT 126, is permanently stored. MSCs 102 and 103 are responsible for the switching of trunk circuits as well as the processing of call setup and mobility management signaling messages. In addition to operating as switches, MSC 102 and MSC 103 also function as telecommunications gateways to PDN 120 and PSTN 130 respectively.
MSCs 102 and 103 perform the necessary switching functions for any compatible MT located within a geographic area associated with a particular MSC, called a MSC serving area. Within cellular subsystem 101, MSC 103 provides call switching functionality between PSTN 130 and MTs 126 and 127. MSCs 102 and 103 also monitor the mobility of their respective served MTs and manage necessary resources needed to effect location registration procedures and carry out handoff functions. Although, in the depicted example, only two MSCs are illustrated in cellular subsystem 101, other numbers of MSCs may be employed depending on the communications system.
Each MT utilizes various radio frequency (RF) channels to communicate with a base station (BS). The RF channels utilized for control functions such as call setup during an origination attempt will be referred to hereinafter as control channels. In CDMA technology, the control channel consists of an access channel for control signaling from the MT, and a paging channel for control signaling to the MT. In contrast, RF channels utilized by MTs to convey voice or other end-user data are sometimes referred to as voice channels, and will be referred to hereinafter interchangeably as xe2x80x9ctraffic channelsxe2x80x9d (TCHs). TCHs may also be delineated according to the source of radio transmission. A Base Station (BS) 125 includes a base station transceiver subsystem (BSTS) 124 and a base station controller (BSC) 123. A TCH for transmitting from a BSTS is called the forward TCH, while a TCH utilized by the BSTS for receiving transmissions from the MT is called the reverse TCH.
HLR 104 is utilized within cellular subsystem 101 to manage mobile subscribers. Subscriber information that associates a serving MSC (MSC-S) with a particular MT is stored in permanent subscriber records within HLR 104. These records contain information such as the serving VLRs 132 and 133, and subscription parameters of MTs 126 and 127. For example, MT identity, Electronic Serial Number (ESN), and subscriber profile data are stored within HLR 104. VLRs 132 and 133 contain a copy of the records of the MTs currently residing within their respective service areas. In addition, VLRs 132 and 133 also keep track of the current location area of each MT in terms of the last accessed cell. This information is only temporarily stored at VLRs 132 and 133 and is removed once the subscribers move out of their respective service areas for a predetermined period of time. Most network equipment manufacturers have adopted a combined MSC/VLR approach such that each VLR is co-located with a MSC.
BS 125 includes the physical equipment for providing radio coverage to defined geographical RF-coverage areas called cells. BS 125 contains the hardware necessary to communicate with MT 126. BSC 123 performs control functions, while BSTS 124 performs the transmitting/receiving function within a given cell utilizing radio transmission/receiving equipment.
The PSTN and other networks include hierarchies of switches that are navigated to provide connections between telephones and other data terminal equipment (DTE). The primary function of a telephony switching system is to interconnect lines or trunks between telephones, DTEs, or other switches. In addition, switching facilities must perform other administrative functions besides switching such as control signaling, route selection, and toll call accounting. Conventional switches, including those incorporated into MSC/VLRs, incorporate some intelligent agent which provides management and control of switch functionality.
There are several problems associated with conventional circuit-switched MSC/VLR implementations such as that depicted in FIG. 1. Scalability of MSC/VLR networks is one such problem. When an MSC""s port, switching, signaling, or processing capacity is exhausted, an entire MSC/VLR unit is often added as the finest increment for increasing network traffic handling capacity. Given this coarse granularity for scaling a carrier""s networks, much of the per-switch dedicated peripheral equipment is underutilized (signaling links, announcement peripheral, conferencing peripheral, etc., for example).
As data traffic continues to increase relative to voice traffic, a conventional MSC/VLR network becomes a less efficient telecommunications management tool. Circuit-switched MSC/VLRs utilize dedicated two-way physical channels in which at least 50% of the allocated bandwidth generally conveys silence and is thus wasted for voice traffic. For data transmission, an even greater bandwidth is typically wasted due to the asymmetric and often bursty nature of data sessions (file transfers, for example). Consequently, carriers often overlay their voice networks with a data network, thereby incurring the costs of operating two networks. Recent developments in wideband wireless transmission have introduced the likelihood that wireless, mobile telecommunications will be increasingly utilized to support multimedia data sessions. Such data sessions will exacerbate current problems with circuit-switched telecommunications.
The nature of conventional MSC/VLR network implementations can result in bottlenecks such as HLR transaction capacity which often limits traffic handling capacity of such networks. As MSC/VLRs are added, mobility-related HLR messaging increases (especially registration signaling), thereby necessitating additional HLRs for such networks. One possible solution within the ANSI-41 network reference model for addressing an excessive HLR transaction load, is to serve multiple MSCs with a single VLR. In most implementations, however, the MSC""s dependence on VLR data renders a decoupled MSC and VLR implementation unfeasible. Finally, a number of efforts have been made, without widespread success, to provide residential, business, and BRI line services to wireless, mobile subscribers.
It can therefore be appreciated that a need exists to address the limitations inherent in conventional circuit-switched MSC/VLR network implementations. Scalable, functional elements that operate in a packet-switched context may be utilized to efficiently accommodate both voice and data traffic, and thus alleviate the aforementioned problems with current MSC/VLR implementations.
It is therefore one object of the present invention to provide a method and system for replacing a circuit-switched network of MSC/VLRs with a packet-switched core network.
It is another object of the present invention to provide a physically decomposed, packet-switched core network for incorporating the voice and data traffic transport and control facilities conventionally provided by networked MSC/VLRs.
The above and other objects are achieved as is now described. An improved method and system are disclosed for providing packet-switched management of switching and handoff functions for a mobile terminal during call setup and user communication phases of a telecommunication session. A radio access network (RAN) including an air-interface transceiver in communication with the mobile terminal is in communicative contact with a packet-switched core network including a plurality of heterogeneous functional nodes. These heterogeneous, scalable nodes in such a core network together provide the functionality that is attributed to multiple MSC/VLRs in a circuit-switched context. Within the core network are wireless access gateways (WAGs) having media channels that provide an interface between the radio access network and the core network. A wireless mobility server (WMS) in communicative contact with the WAGs and anchor packet gateways (APGs), serves as a media gateway controller (MGC) for each WAG and each APG, controlling connectivity of the media channels therein. The WMS also presents the appearance of a single MSC/VLR to the ANSI-41 signaling network, on behalf of other network elements that together provide the functionality of a network of MSC/VLRs. The WMS and APG together hide the mobility and wireless characteristics of the MT on the control and bearer planes respectively. A call server (CS) serves as an MGC for trunking media gateways, and its functionality may be derived from an MSC or Class 5 End Office, depending on the service set to be provided to mobile terminals. A packet-switching network serves as the core network backbone providing packet-switched communication transport facilities between nodes.